1. Field of the Invention
This invention relates to a process for the selective alkylation of the unsubstituted ortho position or positions of phenolic compounds. More particularly, it relates to a process for carrying out the aforesaid alkylation with excellent results and long time stability in the presence of an improved catalyst containing manganese oxide as a main component.
2. Description of the Prior Art
The preparation of 2,6-dimethylphenol, among other ortho-alkylated phenols, has heretofore been the subject of many studies because it is a raw material for the manufacture of polyphenyleneether having a wide range of utility as a heat resisting resin.
Currently, a process for the ortho-alkylation of phenols is in industrial use which involves the vapor phase reaction of a phenol with an alcohol in the presence of an acidic solid catalyst such as alumina. However, in this process, the selectivity in the site of alkylation is insufficient. That is, not only the ortho-positions thereof are subject to alkylation, so that a complicated procedure for the separation and purification of ortho-alkylated reaction products is required.
Another industrial process for the ortho-alkylation of phenol is based on vapor phase reaction in the presence of a magnesium oxide catalyst. However, this catalyst has inherently low activity and requires high temperatures of 475.degree. C. or higher, practically 500.degree. C. or higher, to achieve sufficient reaction.
Moreover, the life of the catalyst is not long enough, so the regeneration procedure must be required in a relatively short period of time for practical use.
In order to solve these problems, there have been proposed many kinds of catalysts, especially those comprising mainly manganese oxide. For example, U.S. Pat. No. 3,971,832 discloses a catalyst comprising mainly trimanganese tetraoxide, Japanese Patent Publication No. 11100/1976 discloses a manganese oxide catalyst which has magnesium oxide or selenium oxide added to it, and Japanese Patent Laid-open No. 32425/1979 discloses the addition of silicon dioxide.
A catalyst comprising mainly manganese oxide has excellent selectivity of ortho-alkylation and high activity; however, the present inventors propose a catalyst disclosed in U.S. Pat. No. 4,227,023 which comprises a mixed oxide of manganese and silicon and one or more additives selected from alkaline earth metals for improving physical strength of the catalyst, and a catalyst disclosed in Japanese Patent Laid-Open No. 76830/1980 which comprises manganese oxide and is treated with alkali metal compound for preventing the depositing of oxygen containing hydrocarbon species onto the surface of the catalyst and for prolonging the service life of the catalyst.
The catalysts exhibit good characteristics as practical catalysts; however, they are still insufficient in effective utilization of alcohols.
The present inventors have undertaken extensive studies for the purpose of overcoming the above mentioned disadvantage in the aforesaid prior art process, and have discovered that mixed metal oxide catalysts with one or more additives included selected from group (A) consisting of germanium oxide, tin oxide and lead oxide are excellent for the improvement of effective utilization of alcohols.